Throttling mud choke apparatus

ABSTRACT

Mud choke apparatus is disclosed, and the preferred embodiment has the form of a hollow, tubular body receiving a mud flow introduced from a lateral port, the flow being directed through an axial passage and past a valve seat. The valve seat is a replaceable, hardened metal liner and is formed with a gradual taper so that the mud flows from the large end through the tapered, smaller end. Thereafter, it flows out of the body through an axial opening. The flow of mud is throttled by a tapered, hardened plug serving as a valve element which is received into the valve seat. A hydraulic cylinder and piston with a connecting rod move the plug. The plug has a surrounding, perpendicular shoulder which seals and seats against a shoulder on the insert to fully close the throttling valve apparatus. Flow is choked by inserting the tapered plug with controlled clearance into the tapered valve seat.

This is a division of application Ser. No. 030,473, filed Apr. 16, 1979,now U.S. Pat. No. 4,281,678 which in turn is a continuation-in-part ofapplication Ser. No. 727,031, filed Sep. 27, 1976, now U.S. Pat. No.4,190,073, and further relates to application Ser. No. 018,508, filedMar. 8, 1979, by the same inventor, now U.S. Pat. No. 4,257,442.

BACKGROUND OF THE DISCLOSURE

As set forth in that application, oil well drilling techniques requirerecirculation of drilling mud. The mud that is normally used in thedrilling process serves as a lubricant for the drill bit, washing awaycuttings as the bit progresses through the earth and carrying thecuttings in a suspended form back to the surface. The drilling mud ismade of a number of products which include abrasive materials and isrelatively heavy or thick. Being laden with a number of particles andunder substantial pressure, drilling mud very often cuts valves andvalve seats of control valves interposed in the mud flow system. Thepresent invention is a flow control choke for use in a mud system. Inparticular, it is a flow control choke which is interposed downstreamfrom the pump before the mud is delivered to the mud pits to control theback pressure in the drill string, itself, and to control the rate ofdelivery of mud to the mud pits.

Various and sundry approaches have been used to the fabrication ofdrilling mud flow control chokes or valves. The present apparatus isdeemed to be an improvement over known structures in that it offers anadjustably positioned, tapered plug cooperating with a tapered seat,both of the members being formed of a hardened material. It has thefeature of fitting the tapered plug into the tapered seat withoutcontact against the sidewalls. Moreover, the throttling surface is notthe surface that provides actual closure in the event that the valve isfully closed. Perpendicular shoulders upstream from the tapered surfacesserve this purpose, yielding the advantage that flow through the taperedplug and seat does not require full closure thereof on the stream andthe consequential erosion that occurs in routine operation. Theapparatus is exposed to mud flow heavily laden with particles whichmight damage, harm or otherwise destroy the equipment. The surfaceswhich provide the throttling effect, therefore, serve only that purpose,while the valve and seat surfaces which provide full shutoff do notserve dual purposes.

One advantage of the present invention is thus the ability of theapparatus to provide continual throttling to mud flow with surfaceswhich are never required to contact one another. This prevents closureof these surfaces against one another with the consequential damage thatoccurs should particulate cuttings be trapped between them. They closetoward one another to achieve the throttling so attractive in thepresent invention, but they do not contact. Moreover, these surfaces areconcentric to one another so that, at a given spacing or throttlingposition, the flow is controlled even though the plug serving as a valvemay be partly worn away. Erosion of the components must be excessive andsubstantially total before it actually modifies the gap or spacingthrough the throttling flow controller.

BRIEF SUMMARY OF THE DISCLOSED APPARATUS

This disclosure reveals an improved throttling mud flow choke apparatuscomprising an elongate, hollow body having a lateral passage where mudis introduced into a central, axial passage. The central, axial passageincorporates a removable valve seat having the form of an internallytapered sleeve. It is made of hardened material and is replaceablebecause it tends to wear rapidly. The apparatus further includes a valveelement which has the form of a tapered plug. The plug and seat taper atthe same angle so that they can fit concentric to one another. The plugis mounted so that it will enter the seat but not contact the valveseat. Maximum penetration is limited by shoulders which areperpendicular to the axis of the plug, one shoulder on the plug facingthe end shoulder of the valve seat. The valve element is carried on anelongate piston rod guided by seals and a bored passage within the valvebody, the piston rod extending to a hydraulic piston and cylinderarrangement for actuation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic control system and improved throttling valve ofthe present invention;

FIG. 2 is a sectional view through the improved throttling mud valve ofthe present invention; and

FIG. 3 is a sectional view through an alternate form of the improvedthrottling mud valve of the present invention particularly illustratingdetails of construction which assist in assembly of the apparatus.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT

Attention is first directed to FIG. 1 of the drawings, where the presentinvention is shown along with the control apparatus for it. The mudcontrol valve is generally identified with the numeral 10 and istypically installed in a duplex arrangement so that two of them areconnected with a common control system. In the event that one failscatastrophically, the other can be used while the first is beingserviced or removed from service. The mud throttling valve of thepresent invention is operated by hydraulic fluid under pressure. Adouble-acting arrangement is preferably used so that it is powered toclose and also powered to open. That is to say, positive control isachieved with a double-acting system. To this end, the apparatusincorporates a fluid line 12 which delivers hydraulic fluid underpressure for the purpose of closing the choke 10. A line 14 is connectedto the choke 10 for opening the choke. The lines 12 and 14 are connectedon opposite sides of a hydraulic piston arranged in a cylinder whichmoves a push rod, all as symbolized in FIG. 1. The representation of thechoke 10 in FIG. 1 is somewhat schematic insofar as the choke isconcerned. FIG. 2 shows greater details. Briefly, a four-port, two-wayvalve 16 controls pressure introduced to the control lines 12 and 14. Itwill be observed that the valve 16 provides high pressure to one chokeor the other. When one is operated to the throttling position, pressureat the other is reduced to enable it to move to the full open position.To this end, the two-way valve 16 connects to a high pressure line 18which provides the input for the two chokes. The valve 16 also directshydraulic fluid flow through a line 20 which returns to a sump. Theremainder of the hydraulic system shown in FIG. 1 is for the purpose ofadjusting the pressure so that closure is achieved. It will be furthernoted that the line 14 provides hydraulic fluid at an intermediate levelwhich forces both chokes 10 full open in the event the high pressure isreduced or switched by the valve 16.

Attention is directed to FIG. 2 of the drawings, where a choke 10 isshown in greater detail. It incorporates an elongate, cylindrical body22 which terminates at a flange 24 which enables it to be connected to amud line. An inlet is provided at a circular, flat face 26, the flatface centering around an inlet passage 28. A groove 30 serves asreceptacle for a ring seal, and a set of threaded bolt holes is alsoarranged on the face 26. Threaded bolts are positioned in the tappedholes at 32.

The elongate body terminates at a cylindrical cavity 36. The cavity 36is closed by a threaded plug 38. The plug 38 is joined to the body toseal the chamber 36. The cylindrical chamber 36 encloses a piston 40which fits snugly within the chamber to prevent blowby and is providedwith a seal ring 42 around its periphery. Hydraulic oil under pressureis introduced through one opening at 44 and acts on one face of thepiston 40. The opposite side of the piston 40 is exposed to hydraulicfluid introduced through a tapped opening 46. The tapped opening 44 isadapted to be connected to the hydraulic line 12, while the line 14connects to the tapped opening 46. These two openings are arranged onopposite sides of the piston. It will be observed that travel of thepiston is limited so that it does not bottom out before reaching the endof travel shown in FIG. 2. FIG. 2 shows the maximum range of movement tothe right. The piston can move to the left, the range of movement beinglimited by contact of the piston 40 against the plug 38.

The piston 40 centrally connects to a piston rod 48 which is aligned inan axially centered passage 50. The passage 50 is larger than the pistonrod 48, permitting the rod 48 to move freely in the passage 50. Thepiston rod 48 supports a number of external grooves extending about itsperiphery which receive and support O-ring seals 52. The number of sealsis subject to variation, depending on pressures of the mud and hydraulicpressures in the choke. The seal rings isolate hydraulic fluid on theleft of FIG. 2, while drilling mud is on the right of the rings. It ishighly undesirable that drilling mud be comingled with the hydraulicfluid used in the system. The seal rings thus wipe the axial passage 50clean and prevent leakage past the seals.

The lateral opening 28 opens into an enlarged, doughnut-shaped cavity 54which is concentric with the piston rod passage 50. It is enlarged toprovide a larger flow area. It terminates at a shoulder 56 which, inturn, centers about an axial passage extending to the end of theapparatus through the flange 24. The axial passage is internally groovedto receive seal rings 58 which are on the exterior of a tapered,sacrificial sleeve 60. The sleeve is hollow and is internally tapered,having a large left-hand end and tapering to a smaller right-hand end.The sleeve 60 is formed of hardened metal to define a wear-resistantvalve seat. It additionally includes an upstream, perpendicular, facingshoulder 62 which is perpendicular to the flow of drilling mud and ischamfered around its outer edge. The shoulder 62 encircles the valvechoke element which is identified by the numeral 64 and has the form ofa tapered, solid plug which inserts into the valve seat. The facingshoulder 62 seats against a protruding, circular enlargement 66 whichfaces and abuts the shoulder 62. The plug 64 has an external face withan angle tapering at the same angle as the internal face of the insertor sleeve 60. The valve element 64 substantially penetrates into thevalve seat, proper. It penetrates, and, as it does, the gap between thetwo closes to a specified minimum such as 0.005 inches clearance, theclearance existing fully around the plug. The plug 64 is formed ofhardened material. Ideally, the plug and the valve seat are polished andground to a relatively smooth surface. The two members are made of ahardened material, such as tungsten carbide particles embedded in asupportive matrix. The angle of taper is in the range of 0.5 degrees to12.0 degrees, ideally 1.0 degrees.

The valve body includes a protruding, circular enlargement 66 which hasa shoulder 68 which faces and abuts the shoulder 62. The shoulder 68terminates at a chamfered surface around the exterior. The enlargement66 is shown in the cavity 54, the cavity being substantially larger sothat mud may flow all around the enlargement 66. The enlargement 66 issupported on an elongate, cylindrical extension of the piston rod 48.The valve element is thus carried on the piston rod 48. It will beobserved that the piston rod extends along the axis of the tool from thepiston 40 toward the valve seat 60. It has a stroke which carries theplug valve element to the fully closed position of FIG. 2 to the left ina retracted position whereby retraction pulls the plug from the valveseat. Travel to the left is limited by the stroke of the piston 40. Itwill be further observed that the enlargement 66 is sized to pass intothe axial passage 50.

The valve seat 60 is a removable and insertable sleeve which terminatesby directing fluid flow into a centrally located, tubular insert 70.This is a wear sleeve having the form of right cylindrical constructionand extending toward the face of the flange structure. This completesthe exit passage for the mud flow after it has been choked. Again, thesleeve 70 is removable so that it can be replaced as required.

Operation of the device should be considered carefully, whichdescription brings out certain features of the present invention. Whenthe apparatus is installed, and presuming that an appropriate hydraulicconnection is made to the fittings 44 and 46 shown in FIG. 2, the piston40 is moved to and fro in the chamber 36 by the introduction ofhydraulic fluid on one side or the other of the piston. As the pistonmoves to and fro, the piston rod 48 is moved. Movement of the rod 48 isconveyed through the valve element 64 which has the preferred form of atapered plug. As the plug is moved to the left in FIG. 2, the gapbetween the plug 64 and the sleeve 60 is increased. This opens the choke10 of the present invention to an increased flow of mud. As it movesfurther to the left, some maximum rate of flow is approached. This isthe rate of flow which is achieved on maximum opening of the plug 64from the tapered valve seat 60.

Throttling of the plug 64 in the tapered valve seat 60 is important tothe operation of the present invention and is achieved by insertion ofthe tapered plug into the tapered sleeve, thereby narrowing the gap. Itwill be understood that the gap has the form of a concentric passagearound the plug. Mud flows through the concentric passage at a ratewhich is dependent, in large part, on the width of the gap or opening.

Throttling of the mud flow is achieved by controlling the width of thegap. The gap can be increased to increase the rate of flow. Conversely,it can be decreased to decrease the rate of flow. As the gap is reduced,the rate of flow is reduced, and the enlargement 66 is brought closer tothe removable sleeve 60. When closure is desired, the facing shoulders62 and 68 are contacted against one another. Moreover, contact of theshoulders 62 and 68 closes the choke 10 completely against further flowof mud. When full closure is achieved, no throttling action occurs inthe gap because the upstream shoulders 62 and 68 prevent mud flow intothe gap. The facing shoulders 62 and 68 are perpendicular to thedirection of flow which is axially of the choke 10. It will be furthernoted that the direction of flow carries the mud from the enlargedcavity 54, between the facing, perpendicular shoulders 62 and 68 andthen into the gap area around the plug 64. It is highly desirable thatthe enlargement 66 be formed of hardened material in the same manner asthe tapered plug 64. Through the use of the hardened material, the lifeof the apparatus is extended.

The present invention yields the advantage that the tapered valve andvalve seat combination limit flow dependent on the width of the gap. Asmentioned earlier, the gap can be narrowed as closure is made, but itdoes not close to zero which would be achieved by contact of the plugwith the valve seat. Movement to the right is limited as depicted inFIG. 2 of the drawings.

The arrangement of the present apparatus with the upstream perpendicularshoulders and the downstream tapered surfaces is notable. This preventsthe capture of particulate material in the gap area. It is relativelyeasy to imagine how a particle of a certain size located in the gap atthe time of closure can be pinched between the plug and sleeve.Preferably, the size of the gap so relates to the gap which is achievedmomentarily between the shoulders 62 and 68 at the time of closure sothat particles of a size to be of concern are not admitted to the gaparea adjacent to the plug 64 as the perpendicular shoulders close to oneanother. In other words, closure of the perpendicular shoulders prior tocutoff of flow through the choke 10 prevents the intrusion of particlesabove a specified size. This size is related to the gap downstream ofthe perpendicular shoulders. Imagine, for purposes of illustration, thatthe gap between perpendicular shoulders 62 and 68 is approximately 0.005inches at which instant the gap around the plug is larger so thatparticles which do pass through the perpendicular shoulders areinevitably washed through the equipment. Conversely, those that do notflow past the perpendicular shoulders do not become a source ofinterference downstream in the gap around the plug body proper.

On opening, the plug 64 travels to the left as viewed in FIG. 2. Whenopened from a fully closed position, the gap around the plug inevitablyincreases as the plug is retracted.

The present apparatus can be serviced by periodic removal andreplacement of the sleeve 60 and the plug 64. This will depend, in part,on the rate of wear of the components. The rate of wear, in turn, isdependent on the pressure across the choke 10, the rate of flow throughthe choke, the pressure on the mud, the extent that particulate abrasivematerials are entrained in the mud and other factors relating to theoperation of the apparatus.

The device can be used in a variety of circumstances, includingvariations of the flow rate by using a very thick wall valve seat and asmaller plug. Conversely, flow capacity can be increased by usingsmaller or thinner walled inserts and larger plugs.

FIG. 3 of the drawings shows a construction which is very similar tothat shown in FIG. 2. The mud control valve 10 of FIG. 2 illustrates inample detail how the mud control valve of FIG. 3 operates. Accordingly,the operation of the valve 100 will be omitted because the componentswhich comprise the valve element and valve seat remain the same. Thereare several differences worth noting which are amply illustrated in FIG.3. The embodiment in FIG. 3 is referred to generally as the mud controlvalve 100.

The mud control valve 100 incorporates a tapered, plug-like member 102formed of a hardened material and terminating at an end cap 104. The cap104 is spot brazed to an elongate rod 106 which has suitable grooves atvarious locations to receive O-rings 108. The grooves and O-rings formseals so that the drilling fluid does not leak beneath the taperedsleeve 102.

The numeral 110 identifies an enlarged, protruding shoulder at the endof the elongate, rod-like member 106. The shoulder locks against thesleeve 102 which is inserted from left to right as viewed in FIG. 3 toassemble the apparatus. Thereafter, a larger ring-like member 112 isnext positioned around the rod 106 to position the perpendicularshoulder 114 for seating against the shoulder 116. This is where closureactually occurs when the mud control valve 100 is fully closed. Onthrottling action, the shoulders 114 and 116 are positioned parallel toone another and are spaced by a distance suitable to enable the taperedplug to operate in the tapered valve seat in the same manner asdescribed relative to FIG. 2 of the drawings. Again, the member 112 ismoved from left to right over the rod 106 in assembling the equipment.

The numeral 120 identifies a lock ring which is next positioned over therod 106. A key 122 is inserted into a slot to be described. Then, therod 106 is threaded into the cylindrical piston rod 124 which connectsto the piston 126, enabling movement to be transferred to operate themud control valve 100 via hydraulic pressure applied to the piston 126.Ideally, the piston is arranged in the cylinder with suitableconnections to make a double-acting system. Lengthwise movement iscoupled from the piston through the assembled structure to therebyposition the tapered plug in the tapered seat in the manner describedbefore. It will be observed that suitable O-rings 128 prevent leakagealong the exterior so that drilling mud is isolated from hydraulic fluidnear the piston 126.

Assembly of the equipment is very important. Disassembly and fieldservice are equally important. Components 102 and 112 tend to wear away,and it is necessary to periodically replace them. Field disassembly,therefore, enables the present invention to be quickly repaired afterthe expected wear has occurred. The wear is occasioned by drilling mudwhich, of course, is very abrasive. The abrasive mud impinges on the twocomponents suffering the most exposure and will wear them away so thatreplacement is inevitably required. Field assembly, while beingimportant, cannot be made so easy that the components become unthreadeddue to vibration acting on the equipment. Catastrophic failures haveoccurred as a result of vibration. The extreme vibration found in theenvironment can, indeed, back threaded members off so that unthreadinginadvertently occurs. This is prevented by the lock mechanism shown inFIG. 3.

The lock mechanism shown in FIG. 3 utilizes a key slot in the rod 106 toreceive the key 122. The key may have a span of perhaps 10.0 or 15.0degrees, referring to the circumference of the rod 106. Accordingly, thekey slot is made to that width with sufficient room to spare so that thekey 122 can be easily inserted. The key, when inserted, locks the ring120 against rotation. In other words, the ring 120 is free to rotate ifthe key 122 is omitted. It fits somewhat loosely around the rod 106.However, its loose connection is merely a convenience to assembly sothat it can be readily rotated. It incorporates a pair of oppositelylocated drilled holes 136 which are sized and spaced to be used with aspanner wrench. The spanner wrench imparts rotation to the ring 120which, in turn, rotates the rod 106 to make it up at the threads 138.The threads 138 are torqued to a required tightness. Thereafter, thering 120 is locked in position by utilizing a set screw 140 which keepsit from rattling around the rod 106. Additionally, another set screw at142 lock it on the protruding shoulder which surrounds the rod 106. Theset screws serve the purpose of holding the ring stationary. They do nottransmit torque when the ring is being rotated. More accurately, theyhold the ring so that it will not wiggle and jiggle during use. Theirhold on the ring assists in prevention of unthreading.

The assembly procedure thus taught in FIG. 3 particularly features thethreading of the ring 120 coupled through the key 122 to make up thethreads at 138. The threads 138 must be torqued to a fairly severestandard; otherwise, vibration may unthread the apparatus at 138. Ifthis were to occur, the valve might lock shut. Moreover, if it occursafter some wear has impacted the equipment, unthreading, coupled withthe wear, may cause portions of the equipment to break, and pieces ofthe plug assembly might easily flow downstream. This kind ofcatastrophic failure is prevented by the connective mechanism shown inFIG. 3. Moreover, it is a mechanism which enables field assembly anddisassembly. For instance, in the field, the mud control valve 100 isrepaired by replacing the worn parts quickly and easily. The equipmentshown in FIG. 3 is disassembled from the left-hand end to remove the rod106 which is unthreaded utilizing a spanner wrench affixed to the ring120. The parts 102 and 112 can thereafter be replaced. They areparticularly the parts which require servicing because they are exposedto maximum wear. In other regards, the mud control valve 100 functionsin the same manner as the mud control valve 10 shown in FIG. 2.

While the foregoing is directed to the preferred embodiment, the scopethereof is determined by the claims which follow.

I claim:
 1. A method of controlling drilling mud flow in a drillingmudchoke which choke includes:a hollow valve body having a passagetherethrough; a valve seat having an encircling, tapered facesurrounding an axial passage for directing mud flow past said taperedface and along said passage within said valve body; an encirclingcircular valve seat shoulder in a plane perpendicular to the flowthrough said axial passage which shoulder defines an upstream locatedclosure face cooperatively positioned relative to said valve seattapered face; a valve element having an external tapered face conformingto said valve seat tapered face wherein said valve element, on movement,moves into a concentric, centrally positioned throttling location withinsaid valve seat opposite said valve seat tapered face and wherein saidvalve element and said valve seat tapered faces define a gaptherebetween for throttling mud flow passing through the gap, andwherein said valve element controllably blocks the axial passage flow ofmud past said valve seat; said valve element and said valve seat taperedfaces are defined by straight line segments in axial section; asurrounding circular shoulder on said valve element which shoulder isadapted to conform to and seat against said valve seat shoulder to plugand close the flow of mud through the gap between said valve element andsaid valve seat, wherein said valve element and valve seat define aminimum gap at closure of said valve element relative to said valveseat; means for moving said valve element into a fully closed positionrelative to said valve seat; inlet and outlet means communicating withsaid passage through said valve body; and wherein the method includesthe steps of:(a) positioning the valve element in the hollow valve bodyand spaced from the valve seat such that the encircling circular valveseat shoulder and the surrounding shoulder on the valve element arefacing one another and moved toward or away from one another on movementof the valve element in the valve body and such movement varies thevolume of mud flowing therepast; (b) further positioning the valveelement in the valve seat to enable the tapered face of the valveelement to move into a throttling position relative to the encirclingtapered face of the valve seat between first and second throttlinglocations relative to the valve seat to define a gap therebetweenwherein mud flow between the tapered faces in the gap is reduced in thesecond throttling position as the gap is narrowed on movement; (c)defining a flow path from the inlet means of the hollow valve body andthen between the encircling and facing circular shoulders, and whichflow path then flows through the gap defined by the valve element andvalve seat facing tapered faces, and thereafter extending along thepassage to the outlet means; (d) selectively closing the upstreamencircling and facing circular shoulders fully to interrupt mud flowtherepast; and (e) wherein the step of closing the upstream encirclingand facing circular shoulders creates a cleaning and flushing floweffect which prevents particles of a certain size in the drilling mudfrom flowing through the gap.
 2. The method of claim 1 further includingthe step of closing the facing and encircling circular shoulders againstone another to create said cleaning and flushing flow thereacross toremove particles below a specified size in the mud flow from between theshoulders so that such particles are not caught between the shoulders atclosure, and further including the step of excluding particles largerthan the specified size from entry into the space between the shouldersduring closing so that the valve element may close toward the valve seatwithout closing on particles susceptible of causing damage to thetapered faces.